The present invention relates to systems and methods for performing integrated power measurement and/or RDSon measurement.
The capability to dynamically measure the power consumption of an electronic system is highly desirable. Some of the benefits include: system fault detection (should power exceed a normal range), engineering power savings (during system proto type development), ability to provide accurate battery life estimates (in a battery operated system). Today's modern electronic systems often utilize switching regulators in order to improve the system power efficiency and reduce heat.
One way to perform power measurement on a particular circuit is to detect the amount of current flowing in the circuit. Previous solutions to measuring the current flow utilize a sense resistor in series with the output, wherein the voltage drop across the resistor is proportional to the output current. The current is measured by sensing this resistor voltage drop. This method works at the expense of lower efficiency, as any voltage across the sense resistor results in a power loss and resulting degradation in the regulator efficiency. Consequently, in order to minimize the power loss, the sense resistor value is kept small which results in poor resolution of low current measurements (due to the low resulting voltage drop across the sense resistor). Also, low value resistors are expensive.
Another method of measuring electric currents is through an integrator. The current is applied to the integrator, and after a period of time the value of the integrated current is examined, and the current value can be determined from the result of such examination. For example, the integrated current can be permitted to reach a predetermined value and the average current is then a function of the time taken to reach that value. Alternatively, the average current is a function of the time taken to reduce the integrated current to zero, with a reference current.
An alternate method for measuring the output current requires the use of specialized output inductors. Most switching regulators utilize external inductors as part of the voltage transformation/regulation loop. It is possible to add a separate set of “turns” around the output inductor which sense the magnitude of the magnetic flux in the inductor. The magnitude of the magnetic flux is proportional to the current in the inductor. Thus, the extra turns provide a means to sense the current flow in the output inductor. While this method does not suffer the efficiency loss of the sense resistor method, it does require the use of a more expensive and non-standard output inductor.
In a parallel trend, active switching devices such as transistors have an on-resistance (RDSon) that affects their operational characteristics. RDSon measurements are difficult to make on Automatic Test Equipment (ATE) during final production test, yet guaranteeing RDSon at final test is important to proper operation of the part. Thus, a self-test ability of the part for RDSon is highly desirable.